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Old 03-07-2016, 08:11 AM
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DJScotty (Scott)
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Coma Corrector fogging up

Hi all. I have a little problem due to the very cold temperatures up here in Brissie lately, to which I have a solution (pulling the imaging train apart mid session and blowing the coma corrector with a hair dryer) but I was wondering if anyone has a more practical solution.

Some context:
The coma corrector (Baader MPCCIII) is inserted into the draw tube of my focuser, so wrapping it with a heater band is not possible....

Thinking about it as I type, IF I wrap the draw tube with a heater band in the right spot, will that heat up the whole area enough to solve the issue? The focuser is a moonlite by the way...

^Thanks for your help...

Scott
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Old 03-07-2016, 09:49 AM
glend (Glen)
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Cold in Brisbane?
What kind of scope is it? An open ended scope like a newt is much more likely to have this problem, and it is made worse if your using a cooled camera, as cold can transfer to the MPCC. A five inch heater strap wrapped around the focuser tube could help but humidity is your big problem. It's less of a problem in an observatory but if your on a tripod on the damp ground your going to be fighting it.
If the scope is a newt and you have a fan on the back this can help keep the air moving over the inter facing surface of the MPCC and may help keep it clear. Most good rear fans can be used while imaging (just mount them on silicon pads if possible and use one with a good bearing). Use a long dew shield on the front if you can (assming its open), this will slow it down. If it is an open truss type scope, even with a shroud, this will be an ongoing challenge. I have heard of people using small plastic scroll fans to push air across mirrors (boundary layer movement) to keep fogging at bay, but you would need to be able to mount it somewhere out of the light path where it can blow across the MPCC lense, or into the focuser tube opening.
Good luck.
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Old 03-07-2016, 09:58 AM
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DJScotty (Scott)
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Quote:
Originally Posted by glend View Post
Cold in Brisbane?
What kind of scope is it? An open ended scope like a newt is much more likely to have this problem, and it is made worse if your using a cooled camera, as cold can transfer to the MPCC. A five inch heater strap wrapped around the focuser tube could help but humidity is your big problem. It's less of a problem in an observatory but if your on a tripod on the damp ground your going to be fighting it.
If the scope is a newt and you have a fan on the back this can help keep the air moving over the inter facing surface of the MPCC and may help keep it clear. Most good rear fans can be used while imaging (just mount them on silicon pads if possible and use one with a good bearing). Use a long dew shield on the front if you can (assming its open), this will slow it down. If it is an open truss type scope, even with a shroud, this will be an ongoing challenge. I have heard of people using small plastic scroll fans to push air across mirrors (boundary layer movement) to keep fogging at bay, but you would need to be able to mount it somewhere out of the light path where it can blow across the MPCC lense, or into the focuser tube opening.
Good luck.
Yeah. Cold. Believe it or not. Getting down to nearly 0 where I live.
It is an open ended newt. I don't have fans on the scope.
I just might give the dew shield a crack.

Plus the heater strap on the focuser.

Thanks for the thoughts Glen

Scott
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Old 03-07-2016, 10:09 AM
glend (Glen)
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And watch for secondary fogging, on newts in those conditions it can be a problem. There are secondary heaters available from places like Kendricks. Kendricks is from Canada and they know cold management. They might have a solution for heating your focuser. I know they sell a rubber sheet type heater that can be used on the back of mirrors, and these can be cut I believe, (they have a heater core), I used their RC secondary heater for a couple of years before I sold the scope.
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Old 03-07-2016, 10:10 AM
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Hi Scott, When I used to have problems with the front of the camera getting too cold I built a heater ring using resistors. Something like this might work for you. This one is 10 x 4.7 ohm (1 watt) resistors in series so total 47 ohms resistance.

Peter
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Old 03-07-2016, 07:58 PM
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billdan (Bill)
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I would steer clear of hairdryers if you are imaging for the following reasons:-

a) The chance of blowing dust onto the optics which will mess up your flats, because half your images will be clean and after using the hairdryer you will get dust motes on the CC and secondary,

b) Heating up the the affected areas will affect your focus and you will be chasing focus as it cools down.

c) It only lasts for 10 to 15 mins anyway and then you are all dewed up again.

As stated above better to use dew heaters, one near the camera and one behind the secondary, and of course a dew shield.

Cheers
Bill
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